Signal-operated indicating device



Dec. 22, 1942. H. HQFMANN 2,305,934

SIGNAL-OERATED INDICATING DEVICE Filed Feb. 18.1939

Patented Dec. 22, 1942 SIGNAL-OPERATED INDICATING DEVICE Heinz Hofmann,Berlin, Germany; vested in the Alien Property Custodian ApplicationFebruary 18, 1939, Serial No. 257,153 In Germany February 18, 1938Claims.

The invention relates to the operation of electric indicating devices,such as glow discharge lamps, telephones or the like by signal voltages,such, for instance, as voltages arriving from marker beacon radiotransmitters in order to enable the pilot of an aircraft or othervehicle to ascertain in well known manner the position of the craft withrespect to the beacon.

The invention consists in certain features of novelty which will appearfrom the following description and be particularly pointed out in theappended claims, reference being had to the accompanying drawing inwhich:

Fig. 1 shows the circuit arrangement of one embodiment of the invention,while Fig. 2 represents the circuit arrangement of an improvement uponthis embodiment,

In certain types of aircraft locating systems, radio marker beams arelocated at predetermined geographical points and when the aircraft ispassing such a point or is travelling on a line directed towards suchpoint, a visual signal and an audible signal are produced to indicatedto the pilot the geographical location of the aircraft. Such knownsystems require grid-controlled amplifier tubes in connection with theradio receiving equipment on the aircraft, one or more of the amplifiertubes operating at a predetermined point on the amplificationcharacteristic curve. However, it is quite apparent that the aircraftmay pass such a marker at a high level or at a low level and theintensity of the signal received on the radio receiver may vary betweenvery wide limits. It is possible with such systems that theamplification power of one or more of the gridcontrolled amplifier tubesin the aircraft receiver will vary depending upon the field intensity ofthe marker signal at the point where it is to be deter mined, thus ifthe aircraft should pass over a radio marker at a low height, the fieldintensity may be many times greater than where the aircraft passes overthe same marker at a greater height. Furthermore, the same disadvantagemay arise if successive markers unintentionally produce different fieldintensities at a given height. One of the disadvantages of such anarrangement is particularly apparent where two separate signalindicators, for example a visual signal (produced by a glow dischargelamp or the like) and an audible signal (produced by a telephonereceiver or the like) are provided on the aircraft. This disadvantage isthen manifested as an apparent time spacing of the two signals and eventhough this spacing may be comparatively slight, it may give rise toconfusion in the mind of the pilot as to which signal to follow. Inaccordance with the present invention, two kinds of signal indicatordevices are used on the aircraft, for example a telephone and one ormore glow lamps. However, one of the amplifier tubes which feeds,thesetwo classes of signal devices is so designed that normally (i. e.when no marker signals are being received) the tube is biasedsubstantially entirely to plate current cutoff or at least to the lowerregion of the amplification curve having very little slope. However,upon the receipt of a marker signal, the signal acts to shift theworking point of the tube to the upper region of steep slope, thusenabling maximum plate current to be utilized for controlling bothindicators regardless of the field intensity of the received markersignal. Within certain limits therefore, the response of the telephoneand the glow lamps are substantially instantaneous and independent ofthe actual field strength of the marker signal at the point where theaircraft passes. This follows from the fact that the amplification powerof the tube is shifted even for very low signal strengths and finally itapproaches maximum plate current. Since the telephone device isessentially a power operated device, whereas the glow discharge lampsare essentially voltage responsive devices, the maximum power output ofthe tube is effective substantially simultaneously on both devices, thusproducing substantially simultaneous indications independently of fieldstrength. Accordingly, the present invention produces two fundamentaladvantages when applied to radio marker systems for aircraft and thelike as follows:

1. The indicating device whether aural or visual, is operated.instantaneously because the amplifier tube is substantially completelyblocked until the controlling device becomes effective.

2. From a definite initial value the system operates independently ofamplitudes since the controlling effect will cause the amplifier tube toincrease gradually to the maximum anode current. This advantage is ofconsiderable importance since the maximum anode current is alwaysavailable for operating the indicating device substantially independentof the magnitude of input signal voltage.

In the arrangement according to Fig. 1 the low frequency signal voltagestaken from the output circuit of a receiver are conveyed over atransformer I to an electron tube 2. Tube 2 while illustrated as of thewell-known pentode type comprising a cathode 2a, a control grid 21), ashield grid 20, a suppressor grid 2d, and a plate 2e, may be of anyother well-known type. The heater filament for the cathode 2a isindicated by the numeral 21. In accordance with well-known practice, thesuppressor grid 2d may be connected directly to the cathode 2a by thewire 2g. The by-pass condensers 2h, 21, are provided across the variousresistances for the well-known purpose of preventing singing in theamplifier. On the .other handtbc..condenserlis a c0up1ing c.on-.

denser of sufficient capacity to allow a portion of the amplified signalwaves to be applied to the rectifier network which includes one-wayrectifier 8, resistance 9 and the resistance in. The resistance 3 beingconnected in the plate-to-cathode circuit of tube 2 imparts a negativebias to the control grid 2b even for extremely small values of platecurrent. The value of this normal plate current can also be controlledin the well-known manner by adjusting the potential of the plate 2e andthe screen grid 20 by means of the respective resistances 4, and 6. Thescreen grid is connected between the voltage dividing resistors 4 and 5.Resistances 3, l, 5, 6 are proportioned in the well-known manner so toadjust the working point of tube 2 that this tube is almost completelyblocked in its state of rest. However upon receipt of signal waves, asmall proportion of the signal voltage flows through the tube 2 and isconveyed from the anode circuit over a condenser T, in order to berectified by a rectifier 8. The continuous or unidirectional voltagearising at resistances 9, I0 serves as control grid voltage for tube 2and in accordance with the invention acts to displace the working pointthereof into the region of steep slope. Consequently the maximum platecurrent will be produced in the output circuit of tube 2 substantiallyregardless of the amplitude of the input signal Waves to grid 2b andtherefore the response of the tube 2 will be substantially independentof the field intensity of the radio marker wave. As a result of therectifier 8 being conductive in the manner indicated by the drawing,that is in the direction of the arrow, when a marker signal is impressedupon grid 2b a portion of the amplified signal flows through therectifier 8 in such a direction that it develops across the resistance 3a voltage drop which is of opposite polarity to the normal negativeblocking bias produced by said resistor 3. In the drawing, the normalbias across resistor 3 is indicated by the full line designations andwhereas the bias resulting from the action of the one-way rectifier 8 isindicated by the dotted signs-tand Included in the anode circuit are theindicating means, such, for example, as glow lamps H, 82 and a telephoneI l coupled to the anode circuit by a transformer [3. As soon as thedescribed regulating arrangement and hence the increase of the poweramplification ratio of the tube 2 become effective the indicating meansll, 12, M will be actuated abruptly. Accordingly, an intensified signalindication is produced so that even weak signals will produce a desiredminimum signal strength.

The arrangement according to Fig. 2 is different in operation from thearrangement represented in Fig. 1 inasmuch as different signal voltages,namely, two different frequencies are conveyed to tube 2, each of whichhas to actuate an indicating device allotted to it. This arrangement maybe used, for instance, if a vehicle, such as an aeroplane, has toreceive the radiation of two marking transmitters one of which ismodulated with the frequency fl while the other is modulated with thefrequency f2. For this purpose oscillatory circuits [5, [6 are arrangedin the anode circuit, one of which is tuned to the signal frequency flwhile the other is tuned to the signal frequency f2. To each of thesecircuits an indicating device is coupled, such as a glow lamp H or l8,respectively. For instance, glow lamp I! is to be operated only by thefrequency I while the glow lamp I8 is only to respond to frequency f2.For each of these indicating circuits,

which are separated from each other by the resonant circuits, a voltageis derived over resistances 19, 2G or condensers 2|, 22. These voltagesare rectified by rectifiers 23, 24 and are employed for affecting thepower amplification ratio of the tube in the manner before stated. Inorder also to provide for an aural indication, a telephone 25 isincluded in the anode circuit.

What is claimed is:

1. In an arrangement for producing substantially simultaneously twodifferent kinds of signals on an aircraft or the like under control of areceived radio marker signal, comprising a visual indicator of the typewhich requires a predetermined minimum voltage level before producing anindication, an aural indicator of the type which produces an indicationfor substantially all levels of voltage applied thereto, each adapted tobe controlled by low frequency signals received on the aircraft fromsaid radio marker, an amplifier tube for amplifying said low frequencysignals, said amplifier tube being normally statically biased so thatthe tube is substantially entirely blocked, and means including anauxiliary biasing circuit responsive to the receipt of a marker signalof any intensity sufficient to produce an indication by said auralindicator to reduce the said blocking bias and thereby to increasesteeply the amplification power of said amplifier tube to produce anindicator control current which is substantially independent of thefield intensity of said radio marker at the point where the indicationsare given, so long as said intensity is sufiicient to produce a responseby said aural indicator.

2. An arrangement according to claim 1 in which the aural signalindicator is of the telephone type and the visual signal indicator ofthe glow lamp type.

3. An arrangement according to claim 1 in which the indications of theaural and visual signal indicators are produced substantiallysimultaneously independently of the field strength of the radio marker.

4. An arrangement according to claim 1 in which the visual indicatorcomprises a pair of glow lamps each of which is coupled to the platecircuit of said amplifier tube through an individual selective filterwhereby said glow lamps respond to their individual signals to producesubstantially simultaneous indications.

5. In an arrangement for producing simultaneously two diiferent kinds ofsignals on an aircraft or the like under control of a received radiomarker signal, comprising two indicators one of which responds inproportion to the intensity of the signal from the weakest to thestrongest, the other of which requires a minimum impressed signal levelbefore it responds, an amplifier tube of the control-grid type foramplifying said signals, said amplifier tube having its control gridnormally statically biased so that the tube is substantially entirelyblocked, means including an auxiliary biasing resistor effective on anyreceived marker signal which is of sufiicient strength to produce aresponse in said one of said indicators to simultaneously reduce saidblocking bias and thereby to increase sharply the amplification power ofthe amplifier to insure that said other indicator produces asimultaneous response whereby the production of the two types ofindications is simultaneous even for very weak field intensities of theradio marker at the point where the indications are given.

HEINZ HOFMANN.

